Structural studies on the thymus of the dogfish, Scyliorhinus canicula L.

Histological and ultrastructural studies of the thymus of the dogfish, Scyliorhinus canicula L., revealed paired lobular masses above the first two gill arches of embryonic and newly hatched dogfish, involuting at approximately 3 weeks. It did not have defined cortex and medullary regions and ultrastructural investigations showed the tissue to be composed mainly of a range of different sized lymphocytes within a connective tissue capsule and reticular epithelial cell framework. Lymphoblasts often in mitosis were also present being more electron lucent and larger than lymphocytes. Macrophages contained cellular debris and frequently whole small lymphocytes. A cell with cytoplasmic granules was occasionally observed.